Atomic Theory and the Atom Chapter 11

Atomic Theory History Atomic Models http://www.brainpop.com/science/matterandchem istry/atoms/

Atomic History Democritus- 440 B.C. Aristotle- 338-322 B.C He proposed that if you kept cutting something in half you would eventually end up with an “uncutable” particle. Which he called an atom Greek: Atomos - indivisible Aristotle- 338-322 B.C He disagreed with Democritus. He believed you would never end up with an indivisible particle.

Dalton- 1808 In search of understanding why elements combine in specific ratios he discovered through his experiments that this happens because they are made of individual atoms. His theory states 3 things 1- Atoms are small and cannot be created, divided or destroyed. 2- Atoms of the same element are all alike 3-Atoms join with other atoms to make new substances

Thomson discovered electrons Thomson discovered electrons. His plum-pudding model described the atom as a lump of positively charged material with negative electrons scattered throughout. Rutherford discovered that atoms contain a small, dense, positively charged center called the nucleus. • Bohr suggested that electrons move around the nucleus at only certain distances. According to the current atomic theory, electron clouds are where electrons are most likely to be in the space around the nucleus.

Rutherford Gold foil Experiment

Atomic Structure https://www.brainpop.com/search/?keyword=Atomic+Model

The Atom Atoms are extremely small. Atoms contain a nucleus. Atoms are made of subatomic particles Protons Neutrons Electrons

Positively charged particles (+). Found in the nucleus. Protons Positively charged particles (+). Found in the nucleus. All protons are identical Each proton= 1 amu (atomic mass unit) Every atom of the same element has the same number of protons.

Particles that have no charge Found in nucleus Neutrons Particles that have no charge Found in nucleus All neutrons are identical Protons & Neutrons are the most massive particles in the atom but located in a very small area (nucleus)

Electrons Negatively charged particles (e-) Located outside of the nucleus in rings or levels called atomic clouds Their mass is so small that it is usually considered zero. It takes more than 1,800 electrons to equal the mass of one proton. However electrons occupy most of an atoms volume.

Parts of the atom

Some things to remember: In an atom, the number of protons equals the number of electrons. As a result, the positive charge from protons equals the number of electrons which makes the atom neutral. All atoms of an element have a different atomic number.

Tells us the number of protons in an atoms nucleus Atomic mass unit = Protons + Neutrons

Atomic Mass Atoms are too small to be measures in everyday untis of mass (grams) Scientist use units known as Atomic mass units (amu) A proton or a neutron has a mass equal to about 1/1000th Atomic Mass is equal to the number of protons and neutrons in an atom.

Isotopes http://www.brainpop.co m/science/matterandche mistry/isotopes/ Isotopes are atoms that have the same number of protons but different numbers of neutrons. Each element has a limited number of isotopes that occur naturally. Some isotopes can be unstable and change it’s composition. We call these radioactive.

ISOTOPES Isotopes of hydrogen and uranium are shown as examples of the isotope notation method Unlike other elements' isotopes, the two heavy isotopes of hydrogen have their own names. Isotopes are atoms that have the same number of protons but have different number of neutrons

Arrangement of Electrons The first ring can only hold 2 electrons The second ring can hold up to 8 electrons The third ring can hold up to 8 electrons Fourth can hold up to 18 Principle quantum model 2, 8,18, 32. Electron Capacity = 2n2 The variable n represents the Principal Quantum Number, the number of the energy level in question. P = N= Valence Shell: last orbital where the “giving” and “receiving” of electrons take place CHEMICAL REACTIONS

Talk about: Is it an Element or Ion? Ions and valence Electrons

• The four forces at work in an atom are gravity, the electromagnetic force, the strong force, and the weak force.

Bohr Model and Flame Lab